ユーザーエージェントは、それぞれの keygen 要素ごとに対して、ユーザー・インタフェースを表示して、ユーザーがこの要素の鍵ペア生成の設定を定義できるようにすることができます。例えば、鍵長などです。

keygen 要素のリセット・アルゴリズムは、これらの各種設定情報をデフォルトに戻すことです。

この要素の値は、次のアルゴリズムから得られる文字列となります：

1. Use the appropriate step from the following list:

   If the keytype attribute is in the RSA state

   Generate an RSA key pair using the settings given by the user, if appropriate, using the md5WithRSAEncryption RSA signature algorithm (the signature algorithm with MD5 and the RSA encryption algorithm) referenced in section 2.2.1 ("RSA Signature Algorithm") of RFC 3279, and defined in RFC 2313. [RFC3279] [RFC2313]

   Otherwise, the keytype attribute is in the unknown state

   The given key type is not supported. Return the empty string and abort this algorithm.

   Let private key be the generated private key.

   Let public key be the generated public key.

   Let signature algorithm be the selected signature algorithm.

2. If the element has a challenge attribute, then let challenge be that attribute's value. Otherwise, let challenge be the empty string.

3. Let algorithm be an ASN.1 AlgorithmIdentifier structure as defined by RFC 5280, with the algorithm field giving the ASN.1 OID used to identify signature algorithm, using the OIDs defined in section 2.2 ("Signature Algorithms") of RFC 3279, and the parameters field set up as required by RFC 3279 for AlgorithmIdentifier structures for that algorithm. [X690] [RFC5280] [RFC3279]

4. Let spki be an ASN.1 SubjectPublicKeyInfo structure as defined by RFC 5280, with the algorithm field set to the algorithm structure from the previous step, and the subjectPublicKey field set to the BIT STRING value resulting from ASN.1 DER encoding the public key. [X690] [RFC5280]

5. Let publicKeyAndChallenge be an ASN.1 PublicKeyAndChallenge structure as defined below, with the spki field set to the spki structure from the previous step, and the challenge field set to the string challenge obtained earlier. [X690]

6. Let signature be the BIT STRING value resulting from ASN.1 DER encoding the signature generated by applying the signature algorithm to the byte string obtained by ASN.1 DER encoding the publicKeyAndChallenge structure, using private key as the signing key. [X690]

7. Let signedPublicKeyAndChallenge be an ASN.1 SignedPublicKeyAndChallenge structure as defined below, with the publicKeyAndChallenge field set to the publicKeyAndChallenge structure, the signatureAlgorithm field set to the algorithm structure, and the signature field set to the BIT STRING signature from the previous step. [X690]

8. Return the result of base64 encoding the result of ASN.1 DER encoding the signedPublicKeyAndChallenge structure. [RFC4648] [X690]

前述のアルゴリズムで使われる data オブジェクトは次の通りに定義されます。これらの定義は、RFC 5280 で定義されているのと同じ "ASN.1-like" 構文を使います。[RFC5280]

PublicKeyAndChallenge ::= SEQUENCE {
    spki SubjectPublicKeyInfo,
    challenge IA5STRING
}

SignedPublicKeyAndChallenge ::= SEQUENCE {
    publicKeyAndChallenge PublicKeyAndChallenge,
    signatureAlgorithm AlgorithmIdentifier,
    signature BIT STRING
}

制約バリデーション： keygen 要素は制約バリデーションから除外されます。

challenge IDL 属性は、同じ名前のコンテンツ属性を反映しなければいけません。

keytype IDL 属性は、同じ名前のコンテンツ属性を反映しなければいけません。ただし、既知の値に限定されます。

type IDL 属性は、"keygen" という値を返さなければいけません。

willValidate, validity, validationMessage 属性、そして、checkValidity() と setCustomValidity() メソッドは、制約バリデーション API の一部です。labels 属性は、この要素の label のリストを提供します。autofocus, disabled, form, name IDL 属性は、この要素の forms API の一部です。